1. Field of the Invention
The present invention relates to a printed wiring board having an electromagnetic wave shielding layer and, more particularly, to single-sided, double-sided or multilayered printed wiring boards having an electromagnetic wave shielding layer.
2. Description of the Related Art
Recently, with the advent of advances in electronic apparatus and appliance technology, and further advances in electronic apparatuses and appliances are hindered due to electromagnetic waves causing more smog and destroying the electronics environment. The electromagnetic interference to electric apparatuses and appliances has also become an important problem.
As a countermeasure for electromagnetic interference, in order to prevent erroneous operation of a circuit due to electromagnetic waves between circuits of conventional printed wiring boards or between outer apparatuses and appliances and the circuit of conventional printed wiring boards, an electromagnetic wave shielding layer is conventionally provided on the whole surface or required portion of the printed wiring circuit through an insulating layer, thereby shielding the electromagnetic wave.
An overcoat layer for guarding the printed wiring circuit is, then, provided on the electromagnetic wave shielded wiring board as an outermost layer. This overcoat layer is formed by using green ink.
Conventionally, an analysis of working condition of the printed wiring board or the insulating layer can be conducted by an electric checker. However, the working condition of the overcoat layer is generally dependent on a visual inspection.
Ink used for the outermost overcoat as outermost layer of the conventional printed wiring board is a thermosetting ink having a comparatively dark green color. As a result the color difference between a green electromagnetic shielding layer of copper paste and the green overcoat layer is very small. Thus, it is difficult to distinguish between the electromagnetic shielding layer and the outermost overcoat layer due to such a lack of color difference and to detect a thin spot in the electromagnetic shielding layer.
Generally, the inks (under resist) used for the insulating layer is also green, in addition to the green overcoat, so that it is difficult to detect blurring of the ink.